Palaeomagnetic Studies in the Scottish Paratectonic Caledonides

Abstract

Presented in this thesis are three studies which document the palaeomagnetic record of rocks forming constituents of the Scottish paratectonic Caledonides. The early Arenig Slockenray Formation within the Ballantrae Ophiolite, southwest Scotland, displays a multivectorial natural remanent magnetisation. Two components (S and M) are identified delineated by differing blocking temperature/coercivity spectra. Component (S) is removed following treatment to 200C/10mT and is regarded as of recent viscous origin. Component (M) forms the characteristic formation magnetisation and resides in both magnetite and hematite. Extensive sampling of all exposed lithologies reveals an (in situ) non-Fisherian distribution of the characteristic magnetisation defining an envelope from SE moderate positive to SW shallow negative directions. A negative intra-formation conglomerate test identifies this component as a pervasive overprint. A second conglomerate test performed on the Benan Conglomerate of Llandeilo age, reveals dispersely directed magnetisations over a stability range equivalent to that of component M. This field test therefore defines a maximum remagnetisation window of 30 million years for the characteristic remanence. Structurally-corrected site mean results from the Slockenray Formation are also non-Fisherian forming a small circle partial arc centred on a vertical axis (NW moderate positive to SW moderate positive diections). A combined palaeomagnetic fold and fault test suggests that acquisition of component M pre-dates both folding and faulting. The resulting palaeolatitude of remanence acquisition (28.8S) implies a tectonic position close to the southern Laurentian margin for the Ballantrae ophiolite in Arenig times. A palaeomagnetic study of the late Silurian - early Devonian St. Abbs Head outlier, SE Scotland, reveals a multicomponent magnetic remanence structure. Three components of magnetisation are recognised termed (L), (I) & (H) pertaining to 'Low', 'Intermediate' and 'High' unblocking treatments respectively, (L: 60